Solenoid actuated fuel injectors typically are controlled by pulses sent to the actuator of a fuel injector solenoid which act to open a fuel injector valve and allow fuel to be dispensed. Such actuators act to displace (via the armature of the actuator) a pintle and needle arrangement of the valve, to move the needle away from a valve seat. In such a state, the valve is open and when the pulse falls there is no power to the actuator and the valve is forced to a closed position.
Pulse profiles may vary and may comprise a series of pulses to operate the solenoid. There may be an initial activation (boost) pulse, provided in order to start to move the needle away from the valve seat, thereafter the pulse and thus power to the actuator is reduced—so therefore after a short while this may be followed by a “hold” phase where a reduced level of power is applied to keep the valve in the open position. These pulses may be regarded as fueling pulses. Thereafter the pulse and this voltage is reduced to close the valve. This may be followed by one or more braking pulses which act to slow the movement of pintle and needle when closing.
So to recap, in order to allow a robust opening, solenoid driven (e.g. gasoline direct) injectors are typically powered up with a slight excess of electric energy to the solenoid coil. The coil is energized in a first phase with a boost voltage to accelerate the armature from close to open. Typically such first phase is followed by a second well defined energy supply (or “hold”) phase, which is characterized to hold the reached open position of the valve for a desired time.
A development trend is to reduce the time from close to open and vice versa of the solenoid driven valve and imitate the performance of competing piezo driven injector valves at significant lower cost. The objective is to dispense precisely lower fuel mass quantities. At very low fueling instances the solenoid driven valve operates in a so called transitional mode as opposed to ballistic or linear mode, which means that the valve will not settle in open position but moves partially towards closing prior to reach steady-state open position. If the closing is initiated during such bouncing it causes dynamically varying closing speeds of the pintle and armature. As a consequence it causes non-linear fueling in relation to the stimulus. Furthermore speed depending dynamic friction is considered to be one cause of accelerated wear, stimulating observable stick-slip effects of the moving parts and can be caused by varying closing speeds stimulated by bouncing. Likewise it comprises insuperable part to part variations if not addressed with significant computational efforts (ICLC). These prior art apparatus have significant part to part fuel variations during this so called transitional phase which limits the usability under these conditions and draw thereby a distinct line of differentiation to competing (piezo) injector propulsion technologies. The technical aspect to address is to control the supply driving schedule of the coil and thereby the speed of the armature and pintle during the transition from close to open and thereby reducing the momentum for bouncing.
It is an object of the invention to overcome these problems.